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Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Saurischia
Suborder: Theropoda
Family: †Abelisauridae
Genus: †Carnotaurus
Species: †C. sastrei

Despite Carnotaurus’ impressive size for an Abelisaurid, its light build makes for a speedy but fragile creature. Carnotaurus is capable of clocking in speeds of over 50 kilometers per hour in short, straight bursts; the massive muscles in its tail that allow it to run at such speeds greatly impede their ability to make sharp turns. Thus, Carnotaurus’ natural habitat is in open spaces, from floodplains near rivers and marshes to the sparsely wooded edges of forests, where they have the greatest chance of running down their prey. In general, these quick predators are nomadic, rarely claiming territories unless they are nesting as they are often pushed out by larger predators. When they do claim territories, they will patrol and mark the territory, both by scraping the bark of trees with their horns or by leaving dung around the perimeter of the territory.

Carnotaurus is a species with pronounced sexual dimorphism in both behavior and appearance. Female Carnotaurus are larger and more aggressive than males, and are often solitary in their young adulthood as they have little tolerance for conspecifics. The males of the species are smaller and more timid, but retain brighter colors and larger horns than the females for use in display rituals. Often, loose coalitions of brothers or unrelated bachelor males will form, and these coalitions work together as a group to hunt larger prey and defend against predators. In these groups, the largest or oldest male will typically take the lead, after displaying his strength with aggressive calls and flashing his throat colors. Rarely, they will engage in ritual combat, similar to when they are courting females. However, these groups will rapidly disintegrate in the presence of a female, with the males readily turning on each other in order to win her affections.

Both male and female Carnotaurus are cagey and skittish towards other carnivores, and are often bullied away from kill sites due to their shyness and fragility, even when in coalitions or pairs. While grouping often bolsters their confidence to a degree, Carnotaurus is a flighty predator that prefers to give up a kill to a stronger animal and hunt again, rather than risk its life to protect its turf. They become more aggressive in the presence of their hatchlings, which they will viciously defend from predation when flight is no longer an option.

Hunting and Diet
In the open floodplains where Carnotaurus lives, speed is king. Carnotaurus makes its living on the run, ambushing and pursuing prey at blinding speed and using its uniquely shaped head to deliver brutal slashing bites. Using this type of hit-and-run strategy, Carnotaurus bleeds its prey to death while avoiding injury.

Due to Carnotaurus’ high speed but weak build, they typically take prey smaller than themselves when alone. Lone Carnotaurus are often seen in pursuit of smaller carnivores, such as Austroraptor, Herrerasaurus, and Utahraptor, or small bipedal herbivores such as Gallimimus and Pachycephalosaurus. Small enough prey is often swallowed whole, using their flexible jaws to pull prey in and force it down their throats. Baby dinosaurs, who are too slow and weak to put up a struggle, are especially prized meals.Small ceratopsids and hadrosaurs, such as Avaceratops and Maiasaura, are also commonly taken, with the speedy Carnotaurus flanking the animal and slashing its sides open with its heavy upper jaw.

Groups of Carnotaurus become more bold, and may try larger and more dangerous prey such as Diabloceratops or Brachylophosaurus. In these situations, members of a group take turns approaching and biting the flanks, legs, and neck of their prey, gouging chunks of flesh out and eating on the run until the creature falls, either from blood loss or from crippling wounds to the leg muscles. From here, the prey bleeds to death, the life draining from it as the hungry group of Carnotaurus feeds.

Carnotaurus eats rapidly and voraciously, gorging itself on meat before any other carnivores can come by and push them off of their hard-earned kill. If they eat their fill before any such predators appear, they will use their powerful back legs to dig a trough and bury any remaining food before leaving and returning to the site as needed.

Solitary Carnotaurus, both male and female, are more inclined to run from many threats than to risk their lives fighting them. Only relatively small dinosaurs, such as single Dilophosaurus, Utahraptors, and Ceratosaurus, have much to fear from a single Carnotaurus. Unrelated Carnotaurus of the same sex are also often in vicious competition, and will chase and threaten one another off of kills and away from territories. Males are slightly more amicable than females in this regard, and will occasionally decide to share food with another male and possibly even form a coalition with him.

Predators of similar size or larger than Carnotaurus are easily able to overpower this lightly-built abelisaurid, and as such, a single Carnotaurus will readily flee from Allosaurus, Baryonyx, and any other carnivore larger than itself. Due to their often overlapping ranges, Baryonyx and Carnotaurus are often in conflict, with the aggressive fish eater rarely even permitting Carnotaurus to drink from its stretch of water. A single male Carnotaurus may also flee from dazzles and packs of Dilophosaurus and Utahraptor, but a female is much more inclined to fight off these nuisances. She has very little tolerance for other predators in her space, and will eagerly kill any scavenger that seems too comfortable in her presence.

When in groups, Carnotaurus gains a bit more confidence, and might try to fight animals that it would ordinarily flee from. Utahraptor packs and Dilophosaurus dazzles become scavenging pests, and Carnotaurus will defend its kills from them and lone Allosaurus or Baryonyx. However, paired predators possess enough strength between them to frighten even a coalition of Carnotaurus, and thus they will still relinquish their kills and flee if it means they will live to fight another day.

Young Carnotaurus are easy prey for opportunistic hunters, such as Austroraptor, Herrerasaurus, and Velociraptor. Thus, nesting parents are often particularly aggressive towards even these small carnivores, and will not permit them to share from their offspring’s food. Without offspring to worry about, however, Carnotaurus typically ignore scavengers unless they are hunting them.

Carnotaurus is a wet season breeder, raising their hatchlings when the land is lush and food is abundant. Females become receptive shortly after the first rains, and their encounters with males from then on are often focused on reproduction. During this time, males will actively seek out females, whether they are in a coalition or not.

Upon encountering a female during the breeding season, a coalition of males quickly dissolves. While ordinarily they might ignore her or run from her, now all of their attention is fixated on her and who gets to mate with her. The males will begin to fight among themselves, headbutting each other and pushing each other with their powerful necks and large horns in an attempt to throw the other male off balance. The fight ends when one male can seize the other by the neck and throw him to the ground. Chronically unsuccessful males often have deeply scarred necks, as a result of years of losses.

Once the fighting stops, the victorious male must impress the female further. Female Carnotaurus are fickle, vicious creatures, and if a male is too forward in his advances, she will turn on him in an instant. It is at this point that the male will begin to court the female, crouching before her in submission and emitting low, rumbling warbles as he arches his back, tilting his head back and pointing his tail up. This displays the bright colors of his neck and tail, indicating his health and maturity. If the female accepts him at this point, he will begin circling her, rubbing his sides along hers in a further attempt to seduce her. If he is successful, they will pair for life. If not, she will quickly end his displays of affection with violence.

While the female is gravid, the pair will seek a secluded area to nest, often near a cliff face to break the wind and block predators. The female will scrape a shallow nest in the soil and lay one to three eggs, which she will then cover with leaves and detritus to help keep them warm. During this time, the female will rarely leave the nest unattended, leaving the male to do much of the hunting and guarding of territory. If something makes it past his watch, the female will viciously guard her nest, readily killing animals that she would usually flee from.

Hatchlings emerge from the egg after several months of incubation, and are small but fiesty. They are already quick movers with a voracious appetite, and will often chase lizards, small mammals, and insects with intent to eat them. Both parents keep a watchful eye on their chicks, but allow them to pursue their own prey as long as they don’t stray too far. However, many chicks are still lost to predators waiting for them to take just one step too far from their parents.

As the chicks grow, they gradually gain more independence. Their parents will eventually leave them within the area of the nest to go off and hunt, entrusting them to remain hidden on their own. If the hunt is successful, the pair will call their chicks over with soft chirps, or bring the carcass closer if it is out of earshot. Later on, the chicks will accompany their parents on hunts, learning from them and even assisting in bringing down small prey. Shortly after this, the chicks will leave their parents’ territory of their own accord, either with their siblings or on their own, in search of their own mate. Typically, brothers will form coalitions while sisters will part ways, preferring to be solitary until they find a mate. With their offspring gone, the adult pair will resume their relatively nomadic lifestyle until the time comes to raise another brood.

Carnotaurus sastrei was a large Abelisaurid from the Late Cretaceous in what is now South America. It was a large theropod, at approximately 9 meters long (30 feet), but lightly built, weighing in at only 1.5 tons (3000 pounds). The only known specimen was found in 1984 in the La Colonia formation, located in modern Argentina, and was incredibly well-preserved. The genus name Carnotaurus means “meat eating bull,” and is a reference to the prominent brow horns on this dinosaur’s strange skull.

Carnotaurus was highly specialised and distinctive, with vestigial forelimbs, long legs, and a short, narrow skull. The skull was deep in profile, with a relatively small mandible, indicating a weak bite. However, it had a very fast, slashing bite, indicating a predilection for taking small and quick prey. In addition, the jaw and mandible were slightly elastic, which would have allowed Carnotaurus to swallow some prey animals whole. However, Carnotaurus was far from a small-game hunter; the strength of its skull suggests that it primarily hunted large prey animals by ambushing them and delivering many vicious, slashing bites until its quarry bled to death. In particular, Carnotaurus was a sauropod hunter.

In life, Carnotaurus was a remarkably fast runner. Its long, thin hind limbs were anchored to the body by a truly enormous caudofemoralis muscle, which was a muscle that connected the thigh bone to the vertebrae of the tail. In most theropods, this muscle was moderately sized, but in Carnotaurus, it made the tail as wide or perhaps even wider than the dinosaur’s hips. This was facilitated by a prominent fourth trochanter, a ridge in the femur that the caudofemoralis attached to, as well as uniquely shaped caudal ribs. The caudal ribs of most dinosaurs and modern animals protrude from the tail vertebrae at a right angle, forming a T in cross-section, but in Carnotaurus, these ribs form a deep V. The cost of this adaptation for speed is that the muscles on top of the tail, which are for holding it steady, are shrunken down. To compensate for this, Carnotaurus’ neural spines locked to one another to hold the tail straight. However, this meant that it could not turn or angle its tail very well, and thus it was likely incapable of making sharp turns while running at full speed.

This wouldn’t have been a serious issue for Carnotaurus, however. In the Late Cretaceous, the part of Gondwana where it lived (now South America) was a vast network of rivers, estuaries, and tidal flats. It would have been too wet for many trees to grow here, with the land instead being marshy and dense with water-loving plants. This meant that Carnotaurus had more than enough room to run and catch prey of all sizes, including its favored sauropods. The climate in this area was likely humid and wet for part of the year and dry for the rest, with seasonal monsoons and droughts.

Carnotaurus coped with these extremes of weather by having no feathers, and instead a fully scaled integument, which was preserved in trace along with the only skeleton ever found of this species. Along its back, Carnotaurus would have had raised scutes similar to those of a crocodile, which may have behaved in a similar way, in that they were both effective bodily armor and a means for the dinosaur to keep its body cool by flushing excess heat and keep its body warm by absorbing heat from the sun.

Perhaps the most interesting feature of Carnotaurus is the feature for which it is named: the two horns placed upon its brow. Research suggests that these structures were used for intraspecific combat, which is to say it used them to fight other Carnotaurus. The strongest theory is that two Carnotaurus would place their heads against one another and slowly push each other, as the top of the head was ill-suited to withstand rapid, sharp blows. This method of combat is similar to many modern deer, rather than rams, and is supported by Carnotaurus’ extremely thick and strong neck muscles. It is likely that these fights took place between males fighting over mates or territory, with the stronger male eventually chasing the weaker out of his space without resorting to killing him.